1. Field of the Invention
The present invention concerns a process for manufacturing fine zirconium oxide powder suitably used as the starting material for zirconia type ceramics.
2. Description of the Prior Art
As the manufacturing method for fine zirconium oxide powder, there is known a method of neutralizing an aqueous solution containing a water-soluble zirconium salt such as zirconium nitrate, zirconium sulfate and zirconium oxychloride with an aqueous ammonia or the like to form a hydroxide sol of zirconium, filtering and water washing the precipitate, followed by drying and calcining, or a method of heating to hydrolyze an aqueous solution of a water-soluble zirconium salt thereby forming a sol, followed by drying and calcining.
In this case, it has been recommended to incorporate an oxide of calcium, magnesium, yttrium or a lanthanide series element such as cerium as a stabilizer in the fine zirconium oxide powder, and such a stabilizer has been incorporated into the zirconium oxide by adding the salt of the above-mentioned metal to an aqueous solution of a water-soluble zirconium salt, or adding an oxide of the above-mentioned metal or the salt thereof at the step of calcining.
The fine zirconium oxide powder thus obtained can be sintered and used as zirconia type ceramics. However, the powder obtained by the conventional method as described above by preparing a sol of hydroxide or oxide followed by drying has a drawback in that coagulated particles are difficult to be disintegrated and can not easily be formed into fine powder and, accordingly, it has a significant effect on moldability and sinterability when it is used as starting material for ceramics failing to obtain a satisfactory sintering product. While it is necessary to uniformly disperse and solid-solubilize the stabilizer for obtaining a stabilized zirconia sintering product, the known method is not completely satisfactory in this regard.
Although there have been proposed, for satisfying the requirement for the zirconium oxide as the starting material for ceramics, a method of minimizing the amount of a hydroxide in the hydrolysis product (Japanese patent Laid-Open No. Sho 58-79818), a method of using an organic solvent for preventing the coagulation upon drying (Japanese patent Publication No. Sho 54-25523), a method of using a spray drier for drying an aqueous solution comprising a zirconium salt alone, or a zirconium salt and at least one salt selected from magnesium, calcium and a metal element having three or higher atomic valency (Japanese patent Laid-Open No. Sho 60-86025), and a method of growing sol particles (Japanese patent Laid-Open No. Sho 61-97134), etc., these methods are not always satisfactory at present.